In 2004 I aquired a French MAS 49/56 semi-automatic rifle.
The guy I bought the rifle from had plenty of cautions for me to follow, that way I knew what I was getting into.
First off was .308 Winchester ammo was forbidden, itd spell doom for this rifle.
So I was sold his remaining stock of wimpy 7.62x51 Argentine ammo, over time I read some about what itd take to tame the 7.62x51 in this rifle.
One thing to NOTE: The MAS 49 series rifles has a insanely heavy floating firing pin that will slambfire soft commercial ammo primers like nobodys business, the best fix is to spend the money and get a titanium firing pin
If you load your magazine with regular primered ammunition, just racking the bolt might start a slamfire event that might only quit when the magazine is empty.
So please take extra care to tame this military beast by getting a proper civilian titanium firing pin in the rifle.
You could try to rinkydink home machine a firing pin return spring on a OEM firing pin, but you still risk a inertial discharge that could cost a bystander their life.
https://phillittleguns.com

https://murraysguns.com/french-mas-4956-firing-pin/

Now down to the meat and potatoes of this.
Thanks to
wombat12Registered User on gunboards

Re: 7.62x51 conversions MAS-49/56 FUSIL SEMI-AUTOMATIQUE (MODÈLE 1949 – 1956)

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#6 Post Thu Sep 14, 2017 6:48 am

Good news-you can get your .308 MAS running with little work and treasure. A few areas overlooked by Century need to be addressed:

1)Recoil spring. For reasons unknown, the recoil spring was shortened. In conjunction with the shortened gas tube, the action of recoil is quite violent. The
recoil spring can be replaced with an original (new) spring available from Gunparts, Inc for $9
https://www.gunpartscorp.com/products/914320

2)Extractor. The extractor is set up for the 7.5 MAS round with a larger rim diameter than the 7.62N/.308. This is why the extractor tends to rip the rims off the .308 rounds. The extractor can be modified to provide a better grip on the .308 case:

https://imgur.com/a/rHlIr#ZURUuEf
File carefully, reinstall the extractor and test by placing the .308 under the extractor, visually inspect and give it a little shake. The .308 case should be held by the extractor.

3) Gas valve. As stated above, the gas system of the MAS49/56 is seriously over gassed for reliability under adverse conditions. Member Starmetal on Gunboards.com offers an adjustable gas valve that is a simple replacement for the original for $38 shipped. I liked mine so well that I ordered one for my 7.5 version. I now don't bother shooters 25 feet down the shooting line!
https://www.google.com/amp/s/www.th...- ... -1956/amp/

https://www.gunandgame.com/threads/my-s ... ide.62078/

https://www.gunboards.com/threads/mas-4 ... ow.415667/

https://www.gunboards.com/threads/mas-4 ... ow.415667/

http://www.surplusrifleforum.com/viewto ... =34&t=3212

http://www.surplusrifleforum.com/viewto ... =34&t=1074

http://jpfo.org/filegen-a-m/masrifle.htm

https://www.gunboards.com/threads/apx-l ... s.1174246/

https://www.gunboards.com/threads/apxl- ... es.128154/


 • Nov 27, 2015

Unless your chamber is really rough, usually the problem with brass sticking in the chamber is a result of too much gas working on the action or the gas getting to the action too soon. When the rifle is fired the brass expands tightly against the chamber walls until the pressure drops sufficiently to allow extraction...if the action gets too much gas too soon the rim will get ripped off or the extractor will break. The starmetal device allows you to essentially shrink the gas port so it takes more time to build up pressure in the gas system, thereby allowing the chamber pressure to drop enough to extract the case.


#5 • Nov 16, 2015
The main problem you are experiencing is because of the higher pressures developed by the 7.62x51 (.308) vs. The 7.5 french cartridge. There is a gunboards member that sold a device that replaced the grenade sight pin (which is a gas cut off) with one that also has an additional allen screw to limit the gas from the barrel. This greatly improved the function of my rifle, allowing me to turn it down so it doesn't slam the action and rip the rims off the brass...I am not going to say that it makes the rifle safe to fire the higher pressure rounds. That's an engineers job.
I believe the gentleman's handle is starmetal. Good luck

I have one and it is great. You can adjust the gas until the fired cases fall at your feet instead of 20 feet away.

 • Nov 27, 2015
Unless your chamber is really rough, usually the problem with brass sticking in the chamber is a result of too much gas working on the action or the gas getting to the action too soon. When the rifle is fired the brass expands tightly against the chamber walls until the pressure drops sufficiently to allow extraction...if the action gets too much gas too soon the rim will get ripped off or the extractor will break. The starmetal device allows you to essentially shrink the gas port so it takes more time to build up pressure in the gas system, thereby allowing the chamber pressure to drop enough to extract the case.

For the DIY gas regulator guy this makes sense.
MrNick
Registered
Joined Nov 2, 2007 
47 Posts
#16 • Dec 14, 2015

I posted this earlier on a different thread but I will post it here. I removed the grenade launcher and taped the hole. I installed 2 allen head set screws. One I set with lock tight and the other was left free to turn. By turning the set screw in and out you change the size of the opening and therefore the amount of gas that passes. Adjustable gas block. I found out how to do this several years ago on this forum. I also polished my chamber with a fired case and compound. Gun works great

Note photo below.
Material you need to remove to get a OEM 7.5 French MAS 49/56 extractor to better grip a 7.62 Nato case extraction rim

The bolt locks against the flat edge of the circular bolt lock pin that is across the back end of the receiver, the bolt locks against this pin to fire, check the milled edge for peening as this affects headspace if batterd all to hell.

https://www.forgottenweapons.com/mas-4956-manual/

https://www.forgottenweapons.com/slow-motion-mas-4956/